1. Field of the Invention
The present invention relates to a cold-cathode type of electron-emitting device. The present invention also relates to an electron beam-generating apparatus, and an image-forming apparatus employing the electron-emitting device.
2. Related Background Art
Cold cathode devices are known as devices capable of emitting electrons with a simple structure. For example, a cold cathode device is reported by M. I. Elinson (Radio Eng. Electron Phys., vol 10, pp. 1290-1296 (1965)). These devices are based on the phenomenon that electrons are emitted by flowing electric current in parallel through a thin film of small area formed on a substrate. Such devices are called generally surface-conduction type electron-emitting devices. The surface-conduction type electron-emitting devices include the ones using a thin SnO.sub.2 (Sb) film developed by M. I. Elinson as mentioned above; the ones using a thin Au film (G. Dittmer: "Thin Solid Films", vol. 9, p. 317, (1972)); and the ones using a thin ITO film (M. Hartwell and C. G. Fonstad: IEEE Trans. ED Conf., p. 519 (1983)).
A typical construction of the surface conduction type electron-emitting device is shown in FIG. 23. This device comprises electrodes 32, 33 for electric connection, a thin film 35 formed from an electron-emitting material, a substrate 31, and an electron-emitting portion 34. Conventionally, in such a surface conduction type electron-emitting device, the electron-emitting portion is formed by electric current-heating treatment called "forming". In this treatment, electric voltage is applied between the electrode 32 and the electrode 33 to flow electric current through the thin film 35 and to destroy, deform, or denature locally the thin film 35 by utilizing Joule heat generated. Thereby, the electron-emitting portion 34 which has high electric resistance is formed, thus the function of electron emission being obtained. Here the state of the high electric resistance results from discontinuity of the thin film 35 in which cracks of 0.5 to 5 .mu.m long are formed locally and the cracks have an island structure therein. The island structure means a state of the film that the film contains fine particles of several tens of angstroms to several microns in diameter and the particles are discontinuous but the film is electrically continuous. In conventional surface conduction type electron-emitting device, voltage is applied to the aforementioned discontinuous high-resistance film through the electrodes 32, 33 to flow current at the surface of the device, thereby electron being emitted from the fine particles.
A novel surface conduction type electron-emitting device in which electron-emitting fine particles are distributed between electrode was disclosed by the inventors of the present invention in Japanese Patent Application Laid-Open Nos. Hei-1-200532 and Hei-2-56822. This electron-emitting device has advantages that (1) high electron-emitting efficiency can be obtained, (2) the device can be readily prepared because of its simple construction, (3) many devices can be arranged on one and the same substrate, end so forth. FIG. 24 shows a typical construction of such a surface conduction type electron-emitting device, which comprises electrodes 32, 33 for electric connection, an electron-emitting portion 36 having electron-emitting fine particles dispersed therein, and an insulating substrate 31.
In recent years, attempts are made to use the aforementioned surface conduction type electron-emitting device for an image-forming apparatus. One example is shown in FIG. 25, which illustrates an image-forming apparatus having a number of the aforementioned electron-emitting devices arranged therein. The apparatus comprises electrodes 42, 43, electron-emitting portions 44, grid electrodes 45, electron-passing holes 46, and an image-forming member 47. This image-forming member is made of a material such as fluorescent materials and resist materials which causes light-emission, color change, electrification, denaturing or like change on collision of electrons. With this image-forming apparatus, the linear electron sources having a plurality of electron-emitting portions 44 arranged between the electrodes 42, 43, and grid electrodes 45 are driven in XY matrix, and electrons are made to collide against the image-forming member 47 in correspondence with information signals to form an image.
The above-mentioned surface conduction type electron-emitting devices exhibit favorable electron-emitting characteristics under a vacuum of about 10.sup.-5 to 10.sup.-9 torr. However, they cause variation of the emitting current to an extent of about 25 to 40% with the decrease of the vacuum degree. If the variation of the emitting current is extremely large, the aforementioned image-forming apparatus, in particular, is seriously affected. For example, an electron beam display apparatus shown in FIG. 25, if the image-forming member is a a fluorescent material, involves problems that (1) the luminance of the fluorescent material becomes irregular owing to the variation of the electron emission quantity of the respective electron-emitting devices, (2) the display flickers owing to the fluctuation of light emission quantity of respective bright spots on the fluorescent material.